A calcium-phospholipid-phosphate complex has been isolated from bone and shown to be present in higher proportions in young developing bone than in mature bone. The role of this complex in the mineralization process is being studied by determining the kinetics of nucleation of hydroxyapatite in metastable solutions. The rates of hydroxyapatite formation in the presence of the complex and in solutions where the complex and enzymes which might trigger release of Ca and/or phosphate from the complex are being compared to the kinetics observed in the presence of hydroxyapatite seeds, non-complexed phospholipids and collagen. Experiments are being initiated to determine the structural properties of the complex and the way in which the complexed-lipids differ from the non-complexed ones. Synthetic Ca-PL and Ca-PL-PO4 are complexes which will be prepared and analyzed by infrared spectroscopy and x-ray diffraction (both wide and small angle). In the case of the infrared studies the infrared spectra obtained will be compared with that of the complex. Preliminary structural studies by x-ray low angle scattering and radial distribution analysis as well as crystallographic methods will be performed to determine changes in lamellar structure, radius of gyration, Ca-C-O interactions Ca-PO4 interactions. BIBLIOGRAPHIC REFERENCES: A.S. Posner, N.C. Blumenthal, A.L. Boskey and F. Betts, Synthetic analogue of bone mineral formation. Jour. Dent. Res., Spec. Issue B; 88-93 (1975). A.S. Posner, N.C. Blumenthal, A.L. Boskey and P.J. Tannenbaum, The formation of bone mineral, in, Calcium metabolism, bone and metabolic bone diseases, eds. F. Kuhlencordt & H.P. Kruse, Springer Verlag Berlin, 1975.